Xara :: Remove Trailing Shadows Shown In First Image

The example I use in this question has already been solved by friendly posters here and this is not a rehash... just using the materials at hand to illustrate the point.The effort here was to remove the trailing shadows shown in the first image (at the included URL below).

In that thread 2 posters showed how to do this using a completely different approach.That is, using Arrange/Apply ClipView..However, I used the help manual to try to do this, at a section headed Combining Shapes

When subtracting, intersecting and slicing, you can either use the topmost selected shape to do the "cutting" of the lower shapes, or you can use a mask.To use a mask to cut shapes, first select the shapes and then turn on mask mode. All objects except for the selected shapes disappear while mask mode is on.

Then draw your cutting shape using the main drawing tools (Freehand Tool, Shape Editor, Rectangle Tool, etc.) or paste the shape if you already drew it and copied it. Then select the Arrange->Combine Shapes operation. The mask shape is used to cut the shapes underneath. I never did see anything describing the details of how to do the cutting with one of the shapes already in the composition so I went the mask route, which is explained there.

So I selected all, then went to mask mode, drew a rectangle (at the right in 2nd screen grab below) then Arrange/Combine shapes/ and none of those selections: Add, subtract, intersect and slice... appear to do a darned thing to the objects.